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Just curious if anyone has an idea if my 6 miles to the gallon is good or bad? It's running just fine. I have not been caring anything heavy for any length of time.

Seems like a 6 cylinder should get a little better?

I average about 17 mpg with my 1950 6400
On a trip from Denver to my home in Montana (650 miles) with about 5000 lbs. on I averaged 17.6 mpg.
But the 235 is not stock

Thats about all you can expect.

Randy, sounds ballpark to me considering the rear ratio you'll have, but if everything is well tuned you might get a wee bit better

and welcome to the garage gg, you'll need to give us a lot more data about that modified 235 that gets better mileage for your 6400 than a 3100

Bill

Have a 270 that runs sweet as can be, but I only pull about 9mpg empty. Havin really low gears in the rear end doesn't help my mileage, but at over 9,000 lbs dry weight there's a definite difference between too much gear and not enough to do the job, so there's a trade off.

its intersting this came up i was just checking mine last week in the dump. 40 mile round trip hauling stone. 3.5 tons in box mpg one day was high sixes and the next day just under 3.5 tons was low sevens. no flat road so to speak of all down hill empty and all up hill loaded. when i used to check it some time ago it would get high sevens to low eights empty.

the ashton gets low sevens to high eights tare wt 11000. lbs no water

the dump 7300 lbs empty

the 40 gets 13.5 on a all out flat run for 650 miles to south bend and back
4400 lbs. empty

i dont believe that for a second. recheck your math.

On several thousand mile road trip in my 52 1 ton with a 235 I got in the 12-15 neighborhood.
17MPG in a heavier slower truck with 2.5 tons load in it is a dream.

Grigg, I agree with you, but I think Ashton's statement sums up my sentiments on the matter a little better. We ran GMC 350 and 450 tank wagons in the 50's and 60's. 6 is a good average number and it could fall from that with a cowboy driver.

When I picked up my 1964 GMC 4000 with 305 V6 I averaged 9.9mpg at 50-55mph and 10.1 at 45-50mph during the 480 mile drive home, all highway and state routes. Truck weighed about 10,000 with an empty 1200 gallon tank bed then. It now weighs 7900 with a 12' flatbed. I haven't checked in-town mileage but it is probably 5-6.

9 MPG with flatbed, got 10MPG once